A variety of balloon catheters are known, such as those provided in U.S. Pat. No. 5,522,882 A and U.S. Pat. No. 7,217,278 B2. Thus, balloon catheters, as they are used, perhaps for the enlargement of pathologically constricted vascular structures in the body or for the placement of vascular wall supports—so-called stents—have an outer shaft with a distal end and an inner shaft nested in it by forming a ring-shaped fluid line, that extends beyond the distal end of the outer shaft. At the distal end of the catheter, a balloon is fastened fluid-tight on the distal end section of the outer shaft at its proximal end in a first fastening zone, and with its second fastening zone at its distal end, fluid-tight to the distal end section of an inner part formed by the inner shaft. Between these fastening zones, the balloon is folded into longitudinal folds in non-inflated condition, so that its outer diameter is as small as possible in this condition. This is the prerequisite so that the balloon catheter with the balloon at the distal end can be slid forward, even through narrow vascular structures or very circumflex vascular areas. After placing the balloon at its site of insertion, a fluid can then be pressurized by the circular fluid line formed between the inner and outer shaft and the balloon can be inflated. Thereby, the longitudinal folds unfold in the direction of the periphery, thereby significantly enlarging the diameter of the balloon.
Because of the type of production and design, the balloons of conventional balloon catheters have disadvantages, which become clear in the following summary of the production process. Thus, as a rule, balloons are produced from an elastically stretchable plastic capillary tube with an outer diameter of, for example, 2.1 mm and a lumen diameter of, for example, 1.5 mm. The thickness of the wall of this capillary thus is 0.3 mm. Its ends are clamped into a retention device, whereupon the lumen is charged with a fluid pressure. Between the clamping points, the work piece is inflated and the wall material is drastically stretched, so that an essentially cylindrical balloon with a wall thickness of, for example, 0.03 mm is created. Starting at the clamped in ends of the balloon blank, the thickness of the wall over the cones at both ends of the balloon, decreases toward the casing wall, approximately by a factor of 10.
In a further processing step, the ends are still calibrated and, for example, brought to an outer diameter of 1.8 mm, as well as a lumen diameter of 1.6 mm. The thickness of the wall is then only just 0.1 mm and is thus still three times thicker than the thickness of the wall in the cylindrical part of the balloon blank.
If balloons produced in this way are now fastened with their ends on the outer shaft or inner shaft of the catheter and folded into longitudinal folds for the non-inflated condition, the ends and cones of the balloon contribute a significantly larger wall thickness than the very thin-walled cylinder casing of the balloon. The folded balloon profile is thus largest at the cones that form the balloon shoulders around the fastening zones. Correspondingly, the stiffness of the balloon is also most strongly developed there. Thus, these very thick end sections of the balloon impede an insertion of the catheter into narrow vascular structures. Beyond that, the stiffness of the balloon cones that are folded into folds makes guiding the balloon catheter around narrow curvatures or branches of vascular structures more difficult. Finally, in the production of the balloon catheter itself it is difficult to fold the cone sections that have thicker walls.
The previously mentioned U.S. Pat. No. 5,522,882 A reveals s stent positioning system with a catheter in which the inflatable balloon has ends that extend step-like. As a result of this, no cone sections of the balloon are to be present axially anterior to and posterior to the stent positioned on the catheter. This is achieved by means of sleeve-like top pieces that are directly adjacent to the stent on the balloon end sections, so that upon inflation of the balloon, the cones essentially turn into radial ring steps. The problem of the variable thickness of the wall and the folding of folds in conventional balloons is not addressed in this publication.
U.S. Pat. No. 7,217,278 B2 teaches an expensive subsequent processing of balloon blanks in that after inflation in the sections of the cones and the thick-walled ends, wall material is mechanically removed to decrease the thickness of the wall. Concerning this, particular attention must be paid to performing this processing step below the glass transition temperature of the thermoplastic plastic material. Overall, the production of such balloons as they are known from U.S. Pat. No. 7,217,278 B2 is thus expensive from a technical perspective.